When
a programmer writes a program s/he creates source code which
is usually compiled into a program. If the program subsequently
needs to be amended then any programmer with the source code
will be able to do this. However without the source code no-one
would be able to make any changes.

So
it is essential that when the bespoke application is completed
that the software house also gives the customer a copy of
the source code. At IT Partnership we do this, but many of
our competitors keep ownership of this vital resource - to
either sell the program on to other companies, or to hold
the customer to ransom for any updates they subsequently request.